Influence of aerodynamic particle size on botulinum neurotoxin potency in mice

Abstract

Objective

For many agents, the aerodynamic particle size can affect both the virulence and disease course in animal models. Botulinum neurotoxins (BoNTs), which are widely known as potential bioterrorism agents, have been shown to be toxic via multiple routes of exposure, including small particle inhalation (1–3 µm MMAD). However, the impact of larger particle sizes on the potency of BoNT has not been previously reported. In this study, we compared the potency of BoNT in small and large particle aerosols.

Materials and methods

Outbred mice (ICR (CD-1^®)) were exposed to BoNT-containing aerosols with differing mass median aerodynamic diameters (MMADs) of 1.1, 4.9, and 7.6 microns. The effects of bioaerosol sampler and inhalation exposure modality were studied.

Results and discussion

Collecting aerosolized BoNT onto gelatin filters or into liquid impingers resulted in equivalent estimates of aerosol concentration. Nose-only and whole-body inhalation exposure resulted in nearly identical estimates of the median lethal dose (LD₅₀). The LD₅₀ for inhaled BoNT increased approximately 50-fold when the median aerodynamic particle size was increased from 1.1 to 4.9 µm, from 139 (95% CI: 111–185) to 7324 (95% CI: 4287–10 891) mouse intraperitoneal median lethal doses (MIPLD₅₀). These results demonstrate the importance of aerodynamic particle size and regional deposition patterns with regards to BoNT inhalational toxicity.

Conclusions

These data will be useful for medical countermeasure development, as well as biodefense preparedness modeling by demonstrating that the estimates of dose and toxicity of an inhaled aerosol containing BoNT can be significantly affected by a range of factors.

Keywords:

• Botulinum neurotoxin
• aerosol
• particle size
• bioaerosol
• median lethal dose
• LD₅₀
• MIPLD₅₀
• mice

Acknowledgments

The authors would like to acknowledge Alec Hail D.V.M., Rebecca Holt D.V.M., Heather Cronin, Tammy Jenkins, James Miller, Stacey Miller, Susan Miller, and Sherry Rippeon of the NBACC Comparative Medicine Group for their outstanding technical assistance and diligent attention to animal welfare, and Angelo Scorpio for critical review of the manuscript.

Disclosure statement

The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of DHS or the U.S. Government. DHS does not endorse any products or commercial services mentioned in this presentation. In no event shall DHS, BNBI or NBACC have any responsibility or liability for any use, misuse, inability to use, or reliance upon the information contained herein. In addition, no warranty of fitness for a particular purpose, merchantability, accuracy or adequacy is provided regarding the contents of this document.

Additional information

Funding

This work was supported by Battelle National Biodefense Institute by the Department of Homeland Security (DHS) Science and Technology (S&T) Directorate for the management and operation of the National Biodefense Analysis and Countermeasures Center (NBACC), a Federally Funded Research and Development Center [grant number HSHQDC-15-C-00064].